Chicago: As the “polar vortex” bringing record low temperatures crept across America on Monday, the cold became so intense that for a time it became difficult to describe.

Some weather forecasters began to simply refer to “dangerous cold” and newspapers published tips on avoiding frostbite and lung damage.

The Chicago skyline is seen beyond the arctic sea smoke rising off Lake Michigan. Photo: Reuters

“If you can stay indoors, please do so,” said Gary Schenkel, executive director of the city’s Office of Emergency Management and Communications. “Everyday activities may not be feasible.”

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On Monday morning it was colder at Chicago airport, a record-breaking 26 degrees below zero - or 42 below with wind chill - than it was at the South Pole, where it was minus 23. The National Weather Service warned that “potentially life-threatening wind chills will continue through [until] Tuesday morning".

A meteorologist in Wisconsin became a minor internet celebrity when he posted a video of himself hurling a pot of boiling water into the wind, only to duck as the droplets turned to snow and blew back on him.

Ice builds up along Lake Michigan at North Avenue Beach as temperatures dipped well below zero. Photo: Getty Images

Practically, the temperature meant that in Chicago standing out of the wind, in the sun, in layers of warm clothes, wearing a warm hat and gloves, the cold grabbed you fast. Breathing deeply was difficult and possibly dangerous. Moisture in the nose stiffened and froze with each breath. Exposed skin soon began to hurt.

Despite a fleet of snow ploughs working on the runways, the airport had cancelled 1600 flights before midday. Most schools were closed and many workers were allowed to work from home. Even the city’s prison system was forced to accommodate the terrible cold, allowing inmates due for release to stay on overnight if they chose.

Polar vortex brings cold weather to the United States

Traffic flowed reasonably well in the city, but snow drifts blown by high winds blocked interstate highways throughout the day and many suburban streets remained impassable.

Around Chicago six "warming centres" were established for homeless people, and the city’s largest homeless shelter, Pacific Garden Mission, prepared to break its record of overnight visitors, 1016, the Chicago Sun-Times reported.

“We will set up mats on the ground and use every available space we can,” said Phil Kwiatkowski, president of the mission.

Staff of Chicago’s Department of Family and Support Services spent the day patrolling areas where the homeless are known to congregate.

“We can’t legally, physically remove somebody from their locations if they refuse to go,” the department’s commissioner, Evelyn Diaz, told the Sun-Times. “If somebody refuses to leave, no matter what, we will know where they are, we will keep close tabs on them.”

By the end of the day four people were reported to have died in the cold, each of them collapsing as they shoveled snow. Hospitals in the area reported cases of frostbite.

As the sun set at about 5pm the city was preparing for another day of similar temperatures.